Something I read concerning our older pickups is that the master cylinder cap has a small orifice to allow air in or out to relieve pressure/vacuum. This constant small change of air is one way moisture is allowed in the system which makes it important to change the fluid every couple of years. Newer vehicles have a diaphragm in the cap to alleviate the pressure changes without changing the air. My wife is a very good brake bleeder assistant!
One other thing, Kent mentioned checking your brake shoe adjustment if you cannot get a good pedal; this happened to me last week. I had already finished with the wheels and had adjusted the shoes to what I thought was a slight drag before I bled the system. After a test drive which showed poor brakes I was about to try rebleeding when I noticed that one wheel seemed out of adjustment. It turned out all four needed a good bit of tightening and the latest test drive went well.
Lee
